1. Field of Invention
The present invention relates to thermoset resin fibres, particularly but not exclusively to thermoset resin fibres for use in the manufacture of fibre reinforced composite materials and composite articles.
2. Description of Related Art
Fibre reinforced composites generally comprise reinforcing fibres in a curable resin matrix. The reinforcing fibres are insoluble within the resin matrix, generally acting to stiffen and strengthen and thus reinforce the resin matrix particularly once cured. Suitable such reinforcing fibres include carbon, glass, aramid, ceramic and others known to those skilled in the art.
The combined physical and chemical properties of the matrix resin and the reinforcing fibres in composite materials are generally such that when the combination is cured, the resultant composite articles have considerable strength and relatively light weight characteristics which enable such components to find many applications in many industries, including the aerospace, automotive, marine and civil engineering industries. The resin(s) and fibre(s) are carefully chosen to produce a composite material and composite article with desired characteristics, as is well known to those skilled in the art.
There are many known methodologies for forming fibre reinforced composite materials and articles made from fibre reinforced composite materials. There are methods that involve the combination of matrix resin with reinforcing fibres prior to placement on a tool or in a mould for cure to form composite articles. Prepregs are pre-selected combinations of reinforcing fibre and matrix resin generally presented in the form of sheets or tapes. The advantages and disadvantages of known prepreg conformations are known to those skilled in the art.
Other methods for the manufacture of fibre reinforced composites include placement of dry reinforcing fibres into a tool or mold and then infusing resin into the fibres using technologies such as Resin Transfer Moulding and Liquid Resin Infusion. Again the advantages and disadvantages of such resin infusion technologies are known to those skilled in the art.
Generally, the matrix resin comprises a thermoset resin, such as an epoxy resin, cyanate ester, BMIs or combinations thereof. In the manufacture of prepregs, the thermoset resins are generally introduced to a layer of reinforcing fibres to either fully impregnate or partially impregnate the layer, according to known techniques. The matrix resin can be introduced to the reinforcing fibre layer in either liquid form to either form a layer of resin on the fibre, to partially impregnate or fully impregnate the fibre layer, or it can be introduced as a preformed layer of resin placed on the surface of the fibre layer. In such prepregs, the matrix resin generally comprises thermoset resin and cure agents to facilitate cure of the thermoset. As a consequence, the shelf-life of such prepregs is limited, often with freezing or refrigeration storage required to prolong shelf-life to a practicable level.
In the resin infusion technologies, the matrix resin is generally introduced in liquid form to fully impregnate the dry fibre layers during cure. Again, the thermoset resin is generally introduced along with cure agents which often in combination with conditions of elevated temperature and/or pressure result in the cure of the thermoset resin within the reinforcing fibre structure and thus the formation of a composite component or article having a fibre reinforced resin matrix.
With such known technologies for the production of fibre reinforced composite articles it is the general aim to prevent or minimise the formation of undesirable air pockets or voids within the cured fibre reinforced composite article as these present weaknesses within the finished article. When uncured prepregs are placed in a mould or tool to form an article, it can be desirable for a number to be stacked on top of one another. Often air gets trapped between the layers and various technologies exist that assist in the removal of these air pockets during the cure process. However, these can involve complex and expensive processes and apparatus, such as autoclaves to produce the necessary conditions to drive the air out from between the resinous layers.
Other forms of composite material do not contain fibre reinforcement. For example, resinous adhesives often comprise a combination of liquid thermoset resin with other constituents such as cure agents, catalysts, hardeners etc. To avoid premature cure of such materials the thermoset and the curatives are often kept separate until the adhesive is needed. However, this can be inconvenient, and it can be advantageous for the thermoset and the curatives to be provided together in accurately predetermined amounts, but this generally results in relatively short shelf-life.